Internal plane layers are only for power and ground nets, you can't place traces on them. You should be using a polygon pour instead.
V&J is right. Maybe change the internal plane layers into signal layers and then you should be able to route on them. Also, in case you didn't do it or for others that don't know, for a 4-layer board with blind vias on outer layers you need to make the outer layer pairs the core style and have the pre-preg in the center.
I have come across a situation with unexpected (and certainly undesirable) behavior. The issue has been observed by other users, but no solution has been proposed, as explained below:
The project is a 4-Layer design (Top, L1, L2, Bottom) where L1 and L2 are designated as "Internal planes". I am trying to route signals from a BGA device on the Bottom Later to the Internal Plane L2. To achieve this, I have placed u-Vias directly at the center of the BGA pads. The intent is that these u-Vias take the signal from the Bottom Layer to L2, and then I route them on the L2 Layer. For the layers, I have specified two sets of Drill-pairs; the default (Through Via) which goes from the Top Layer to the Bottom Layer, and for the u-Vias going from L2 Layer to the Bottom Layer.
The strange behaviors that I see are listed below:
1) When I select the L2 Layer, as soon as I start interactive routing, the software jumps to the Bottom Layer and adds whatever trace I draw to the Bottom Layer
2) If I try to change the properties of the trace that is added in Step 1) above so that it is placed on the L2 Layer, the net selection does not remain. For example, when I edit the properties and assign the GND net to the selected trace, I click OK to save the editing. Then, when I check the properties, the net is shown as "no net", as if I never edited the property
Can anyone provide some suggestions or workarounds?
Thanks in advance,